The Proterozoic magmatic and metamorphic history of the Banded Gneiss Complex, central Rajasthan, India: LA-ICP-MS U-Pb zircon constraints

The Banded Gneiss Complex (BGC) of Rajasthan (NW India) is generally thought to be an Archaean basement terrain that was partially reworked during the Palaeoproterozoic. In the central Aravalli mountains the BGC comprises the inferred Palaeoproterozoic granulite-facies Sandmata Complex (charno-enderbite plutons and supracrustal rocks) and the amphibolite-facies Mangalwar Complex (felsic orthogneisses, amphibolites and supracrustal rocks) of presumed Archaean age. Laser ablation ICP-MS U-Pb dating of zircon domains shows that: (a) granulite-facies metamorphism and charno-enderbite magmatism in the Sandmata Complex were synchronous at ∼1720 Ma; (b) igneous protoliths to migmatitic felsic orthogneisses in the Mangalwar Complex have similar emplacement ages as the Sandmata Complex charno-enderbite suite; (c) protoliths to a metasediment from the Sandmata Complex and the Mangalwar Complex were both deposited in the Proterozoic, not the Archaean as previously believed; (d) isotopic disturbance of igneous zircon, and limited growth of new zircon occurred at ∼950-940 Ma, which is tentatively suggested to date amphibolite-facies re-working and anatexis. These data raise questions about whether the BGC in the central Aravalli mountains can be correlated with an apparently similar terrain further to the south, whose magmatic and orogenic history is Archaean.